In recent years, a printer which prints high definition images, such as a photograph of man's face, to a comparatively small print medium, such as an ID card and a bank passbook, is known. This printer uses the ink ribbon. The ink ribbon has color ink which is fused by heating and is applied to a ribbon-like resin film. In this kind of printer, an intermediate transfer film and the ink ribbon are overlapped and conveyed, for example, the color ink of the ink ribbon is fused by a thermal head, and the ink of each color is transferred on the intermediate transfer film. And then, the printer prints a color image on the print medium by transferring the ink transferred on the intermediate transfer film to the print medium.
One end of the ink ribbon is wound around a supply axis, and the other end of the ink ribbon is wound around a rolling up axis. The ink ribbon supplied from the supply axis passes the thermal head and is wound around the rolling up axis. When the ink ribbon is sent out from the supply axis side, the ink ribbon sent out exfoliates from the ink ribbon of rolled form wound around the supply axis. At this time, static electrical charge by stripping is produced in both the ink ribbon of rolled form wound around the supply axis and the ink ribbon sent out.
Such electrification of the ink ribbon tends to differ in polarity with the surface and the back of the ink ribbon. And a quantity of the electrification which is generated when the ink ribbon is exfoliated differs depending upon combination of the overlapping ink colors when the ink ribbon was wound around the supply axis. A diameter of a roll of the ink ribbon wound around the supply axis becomes small gradually as the ink ribbon is sent out. Thus, although a color pattern of a longitudinal direction of the ink ribbon has regularity, the overlap condition of the colors of the ink ribbon wound is irregular. Accordingly, the electrification characteristic of the ink ribbon sent out from the supply axis also becomes irregular.
On the other hand, the thermal head carries out printing by the peeling-off during hot state which exfoliates the ink from the resin film before the temperature of the ink falls. Generally as the thermal head, a near edge type thermal head or a corner edge type thermal head is used. It is known that electrical discharges based on Paschen's law will often arise between the ink ribbon and the thermal head when the electrically charged ink ribbon passes the thermal head. The electrical discharges often arise a problem of destroying the thermal head. For this reason, in prior to a stage where the ink ribbon passes the thermal head, it is necessary to remove the electrical charge charged to the ink ribbon to such an extent that the ink ribbon does not produce the electrical discharge between the ink ribbon and the thermal head.
Following methods are known as a neutralization method for removing the electrical charge charged to the resin film. 1) A method for spraying ionized air on a film in a high voltage alternative ionization chamber is disclosed in JP, P2006-216453A, and JP, P2002-236331A, for example. 2) A method for generating ion by contacting a conductive roller connected to a high voltage alternative power supply to both surfaces of a film and producing electrical discharge is disclosed in JP, PH07-142187A, for example.
However, a neutralization apparatus using a high voltage power supply needs a control system, an electrode, a blower, etc., and needs a comparatively large installing space. This kind of neutralization apparatus needs an initial facility cost and a high running cost. For this reason, it is difficult to use such a large-scale neutralization apparatus for a comparatively small table type printer using the ink ribbon mentioned above.